1. Field of the Invention
The present invention relates generally to a variable displacement wobble plate type compressor provided with a variable angle wobble plate mechanism housed in a crankcase and a built-in type wobble angle control valve arrangement capable of automatically changing a compressor displacement in response to a change in a refrigerating load in an air-conditioning system in which the variable displacement wobble plate type compressor is accommodated. More particularly, it relates to a crankcase pressure control system incorporated in a variable displacement wobble plate type compressor for maintaining a fluid pressure in the crankcase at a level at which a smooth change is made in a wobble angle of the wobble plate mechanism when a refrigerating load is low.
2. Description of the Related Art
A pending U.S. patent application No. 856,760 of the same assignee as the present patent application, filed on Apr. 28, 1986, now U.S. Pat. No. 4,685,866 discloses a variable displacement wobble plate type compressor with an improved wobble angle control unit by which a smooth return of the wobble plate from the least inclined position thereof to a fully inclined position is attained. The compressor disclosed in the pending U.S. patent application No. 856,760 can be operated at a wide displacement range i.e., from the extremely small displacement state to the full displacement state, and therefore, the compressor can be operated so that the compressor displacement is always set at an optimum condition in accordance with a change in the refrigerating load applied to the air-conditioning system. The inventors of the present application have continued their investigation into the performance of a wobble angle control unit of a variable displacement wobble plate type compressor on the basis of the control unit of the pending U.S. patent application No. 856,760. As a result, the present inventors of the present application succeeded in contriving another wobble angle control unit of a variable displacement wobble plate type compressor, which unit is definitely different from that disclosed in the pending U.S. patent application No. 856,760, and functions to enable a smooth change in a wobble angle of the wobble plate mechanism from a larger wobble angle position thereof, that is, an inclined position of the wobble plate to the least wobble angle position, i.e., an erect position of the wobble plate when the compressor displacement must be decreased in response to a reduction in the refrigerating load or a reduction in a discharge pressure of the refrigerant from the compressor due to lowering of the environmental temperature.